基質輔助雷射脫附游離法機制探討- I.陽離子生成與陰離子生成之關係 II.自由電子對陰離子生成之影響

Translated Titles

An Investigation into the Mechanism of MALDI- I. The Correlation between Cation Formation and Anion Formation II. The Effect of Free Electrons on Anion Formation





Key Words

質譜儀 ; 基質輔助雷射脫附游離法 ; 雙極性質譜儀 ; mass spectrometer ; matrix assisted laser desorption ionization ; MALDI ; dual-polarity mass spectrometry



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Chinese Abstract

基質輔助雷射脫附游離法是一個軟性的質譜儀游離源。在一九八零年代被發展出來之後,立刻在各分析領域獲得廣大的應用。然而其機制至今仍然未明。本研究以能夠同時偵測正負離子的雙極性質譜儀做為工具,比較基質的正負分子離子的生成,以獲得一些能解開機制的資訊。 第一部分的實驗觀察樣品晶塊大小對正負離子強度比例穩定度的影響,經過統計分析後,我歸納出兩點。1、晶體構型對基質分子正負離子的生成有顯著影響,但如何影響則不在本研究討論範圍。2、基質的正負分子離子生成無顯著相關性。 第二部份的研究則觀察基質正負分子離子強度受雷射強度變化的影響。陰離子產生的能量閥值較陽離子低。這個實驗結果和第一部份實驗的結論”基質的正負分子離子生成無顯著相關性”符合。為了驗證”基質分子陰離子可藉由捕捉光電子生成”之想法,我將靶材以不導電的玻璃取代原本的不鏽鋼,以減少光電子的釋出量。結果陰離子閥值較低的現象不復存在了。由此可推論基質分子陰離子可藉由捕捉光電子而生成。

English Abstract

Matrix assisted laser desorption ionization (MALDI) is a soft mass spectrometry ion source. Since invented in the 1980’s, it has been wildly used in various fields. However, its mechanism remains quite unclear. This mechanistic study is done with Dual-polarity time-of-flight mass spectrometer (DTOFMS), which can simultaneously detect both polarities of ions produced in MALDI. In the first part of this work, the variation of anion to cation ratio is monitored in crystallized and decrystallized sample. The variation of the two samples are obviously different. There are two conclusions in this part: (1) crystallization condition of the sample has an influence to the formation of both polarities of the matrix molecular ions. (2) The formation pathways of two polarities of matrix molecular ions are lowly correlated. In the second part of this work, I monitored the laser fluence dependency of the intensity of matrix molecular cation and anion. It was observed that matrix molecular anion formation has lower energy threshold. This observation is consistent with the conclusion in the first part, i.e. the formation pathways of two polarities of matrix molecular ions are lowly correlated. Next I adopt a piece of glass, which is an insulator, as a sample support. It was observed that the energy threshold of matrix molecular anion is no longer lower than that of cation. Therefore it can be conclude that matrix molecular anion may form by direct capture of photoelectron in plume.

Topic Category 基礎與應用科學 > 化學
理學院 > 化學研究所
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